Many devices are known for dispensing molten thermoplastic materials, such as the devices described in U.S. Pat. Nos. 3,204,828 and 3,298,572.
Generally, such devices comprise a barrel member having an internal melting chamber which communicates with an outlet opening through a nozzle, and a sleeve with a through opening having one end secured to the barrel member with its through opening communicating with the end of the melting chamber opposite the nozzle. The sleeve is adapted to receive an elongate cylindrical block of solid thermoplastic material which fits closely within the through opening in the sleeve, with one end portion of the block in the melting chamber and the other end portion projecting through the sleeve. Means are provided for heating the barrel member to melt the end portion of the block therein, and means are provided for affording pressing the block through the sleeve and into the melting chamber to force molten thermoplastic material out of the melting chamber through the nozzle.
While such devices function effectively, certain problems can arise for the operator of such a device when he wishes to dispense molten thermoplastic material onto a substrate that will be damaged by molten thermoplastic material at the temperature that such molten thermoplastic material achieves in the melting chamber when molten thermoplastic is not dispensed from the device for a period of time while the means for heating the barrel remains activated. One example of such a problem is when molten thermoplastic at a temperature in the range of about 390.degree.-400.degree. Fahrenheit is applied to adhere expanded polystyrene to itself or other objects as is common in the florists trade, which will result in partial melting of the expanded polystyrene.
The thermostat in the device could be changed or could be made adjustable so that the temperature of the molten thermoplastic material in the melting chamber could be lowered to around 350.degree. Fahrenheit which materials such as the expanded polystyrene can withstand. The former approach, however, is time consuming, the latter approach adds greatly to the cost of the device, and both approaches result in a device with less melting capacity than may be desired after the temperature is lowered.
Also, a large amount of adhesive may be dispensed through the device to lower the temperature of the adhesive being dispensed to a more acceptable level due to a limited dwell time in the melting chamber. With this approach, however, a large amount of the initially dispensed adhesive is too hot for use and must be wasted.